A Picaxe TNC

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smokelight101

Member
Over the course of the summer a few close friends and I started an endeavor to launch a high altitude weather balloon load with a few cameras in hopes to acquire a picture of the edge of space. I know safety flags of the legality of this project are racing. This project is completely legal as it is being built under the specifications set out in part 101 in faa regulations. But this doesn't mean I don't wanna hear your concerns please if you have any voice them.

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&rgn=div5&view=text&node=14:2.0.1.3.15&idno=14

Anyway to the picaxe portion. I plan for a picaxe or a set of picaxes to trigger the cameras, log some sensor data, and work as a TNC for a radio. The TNC takes a string of data from the gps then places it into a standardized protocol that amateur radio hobbyists use for tracking called APRS.

The questions I have.

1. Has any one have any experience with APRS or AX.25?
2. The radio uses different tones for ones and zeros. For example 1400hz for 1 and 2200 for 0 I believe for APRS. I may have the 1's and 0's fliped. Is it possible to do this with the picaxe?
3. When connecting the picaxe to the radios mic in and speaker ports what type of circuitry do you recommend? I was just thinking a resister and capacitor on the mic and a 800 to 8 ohm signal transformer on the speaker for impedance matching but I'm rather novice.

Wow that was alot. Any comments would be appreciated!!!! :)
Thanks for all the help,
Tyler Berezowsky
 
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westaust55

Moderator
Not answering your sepecific questions, but a thought/question of my own as food for thought.

How are you keeping the equipment warm for very high altitudes? :confused:

When on aircraft flights, one can see that the outside temperatures are down to -50degC to -60 degC :eek: (like Ozernoe in Siberia in Winter) and that is in reality just a few kilometers above sea level.
Minimum ambient temperature for the typical PIC chips while energized is -40 degC. I would guess at those sorts of temperatures, that the PIC clock speed would potentially slow down which could lead to error in timing and comms baud rates.
 
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Dippy

Moderator
I know nothing about all this, but is a really nice project and good luck with it.

Just a question about the radio.
Is this radio a ready-made off-the-shelf transceiver?
You mention "mic in"?
And you are going to generate the tones with PICAXE?
Will it be happy with square wave or will you have to filter it to smooth it?
 
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MFB

Senior Member
You should find some useful information in the following free ebook http://www.parallax.com/tabid/567/Default.aspx

There was a PICAXE based article in the February 2007 issue of Elektor magazine by Mike Bessant, that sent data at 1200bps over the audio channel of a 2.4GHz video link using FSK modems.

Also. I have submitted a couple of FSK modem related items under the projects section that might be worth looking at.
 
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smokelight101

Member
Thanks you guys for your thoughts.

Westaust55 - The ridiculous low temperature that are experience nearing -70 degrees Celsius ,and most likely lower at times, is one of my biggest concerns too. A timing error could be the fatal flaw of the hole project crippling the tracking system and if the balloon drifts out of range, it would never be recovered. I've read over the reports of many other projects, simple insulation and self generated heat from the electronics was enough for others keeping it in the toasty room temperate range. Still I'm going to use a crystal oscillator and carve out a high density foam block for minimum heat loss :). Someone from the team wants to place the electronics under testing from ground level. Liquid Nitrogen!!?

Dippy - Thanks for your kind words!! Yes currently were having an old ht transceiver donated. It will be stripped of all the non-necessary components. I'm hoping to be able to use the picaxe for generate the tones, who would wanna build to separate oscillators? :) The square wave vs sine wave delima. In honesty I do not know. Experimentation and research is key here and I have been asking that one around quite alot. The APRS protocol uses the bell modem 202 type modulation at a whooping baud rate of 1200. I don't really see a problem with a square wave at thous speeds but for sake of cleanliness and reliability I'm gonna throw a few filters at it and shape it up.

MFB- Thanks for the link, sending data via the audio line was genius!! I'll make sure to look up your posts!

Eclectic- The pong posting is pretty interesting with regards to its battery. Someone else on the team is tackling suitable batteries. I'll be sure to send him this! I think right now his opinion for the disposable lithiums energizer batteries.

Hope I answered all your question, As the project progress I could keep you guys updated if you want? I'm sure I'll be back here when the programming begins :).
Best Regards,
Tyler Berezowsky
 
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westaust55

Moderator
Yes, liquid nitrogen might be easier than a trip to Red Dog gold mine in Alaska during winter where it gets down to around -50 degC. I recall speaking with the guys who built the Red Dog plant when I was doing work for the Ozernoe Lead-Zinc project in Siberia. They left the dozer engines idling all the time when cold as it was too much work to re-warm a cold engine. Their guide line was people will work to -15 degC (maybe just to keep warm), things stop at -40 deg C, and things just snap at -50 deg C.

As you suggest well insulated in a small space and a small/fractional Wattage may well be enough to keep things warm enough. Should be possible to research/calculate heat input required to keep the chips externally at around say 15 deg C. Should be similar to heat sink and air conditioning theory if you know the thermal resistance of the insulating material.
 
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MFB

Senior Member
The Near Space ebook provides lots of tips on adding thermal insulation etc.

Regarding the Elektor link, that was for a model rocket. Although you could also use 2.4GHz for your application the range would be less than that of a 433MHz transmitter at the same power.
 
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John West

Senior Member
MFB said:
The Near Space ebook provides lots of tips on adding thermal insulation etc.

Regarding the Elektor link, that was for a model rocket. Although you could also use 2.4GHz for your application the range would be less than that of a 433MHz transmitter at the same power.
Click to expand...
If he is using Amateur radio gear I can vouch that a 1W xmitter on 70cm CW can be heard for hundreds of miles in every direction. Altitude is a wonderful thing for Line-of-Sight communications.

A possible advantage to using 2.4 GHz is that extremely high gain receive antennas (Yagi-Yuda) are much smaller and easier to handle at that frequency - more than making up for the loss in absolute efficiency over the lower freqs.. Better for direction-finding as well when the time comes to find the bird.

I got involved with the Denver Colorado Edge-of-Space group on one of their balloon flights. Great fun - and amazing video from 100 thousand feet - although they were tracking it with a 20 meter dish antenna. Something not many of us have access to on a regular basis. ;)
 
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Dippy

Moderator
Just some completely-non-expert thoughts.

All this stuff about 2.4GHz....
1) How high is Tyler's balloon going?
2) What's the best range of low/medium cost 2.4GHz stuff?
(with various antenna configs).
3) If the balloon is going miles up how will you know where to point your Yagi or dish?
(Unless the balloon is SO big that you can see it or have some fancy tracking).

Without a healthy budget and expertise it maybe a good idea to keep to lower Fqs and lower/slower tech.
Plus the fact, he has already been given a transmitter... so, unless there is good reason, maybe all this is a red herring tangetialisation? :confused:
 
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MFB

Senior Member
Dippy: Regarding your point 3, the technique we used when tracking research balloons over the Midlands and North Wales from (the old R101 airship base) at Cardinton Bedforshire was to aim the antenna for peak signal strength. There was certainly little possibility of aiming at a visual target.
 
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Dippy

Moderator
Oh I see, so you have to sit their waggling your plonker until you pick up a signal. Fair enough.:)

Out of interest; what sort of radio gear and what sort of distances? Are they appropriate to this project?
 
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MFB

Senior Member
Yep, that’s about it. Nothing very fancy, just a bloke with a directional antenna looking at a signal strength meter. I certainly didn’t find it difficult because we tracked from launch and knew which direction to ‘waggle’. I suppose you can make things more complicated (PICAXE, servo etc) but balloons don’t change direction fast and tracking angles decrease with distance.

I don’t remember much about the UHF telemetry equipment because it was the only bit of the payload that we did not have to develop. Access to rather unreliable radar information was available but today’s onboard GPS repeaters should make aiming the receiving antenna easer.
 
slimplynth

slimplynth

Senior Member
Out of curiosity and i'm not suggesting sending mi grandad's best thermos filled with picaxe's into space on a balloon but what issues/restrictions would prevent sending a vacuum insulated package onwards and upwards? (weight/pressure?)

Aside from construction difficulties; surely a vacuum would be the best barrier to keep the heat in?
 
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Dippy

Moderator
Surely, you've answered your own question?
"Aside from construction difficulties..."

I have never done any of this, but I would wonder whether it was worth going OTT keeping in mind "construction difficulties".
 
slimplynth

slimplynth

Senior Member
I guess that's the advantage of working as a team though. A welder/sheet metal worker/fitter/tool maker might struggle to comprehend how to even make an LED blink but know straight away how to do something that looks impossible for a 'techno whizz'

Anyway... the thermos has disappeared from sight now - heads up ;) and back to the drawing board of make believe.
 
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smokelight101

Member
Thanks guys for the links.

We will be tracking the balloon at 144.390 MHz The north american freq for the APRS system. Between the elevation point, 5 watts of power and the number of repeaters for the APRS system, I'm fairly confident yet still worry of course haha.
 
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graynomad

Senior Member
Check out this Sparkfun entry

http://www.sparkfun.com/commerce/news.php?id=389

They talk about some of the issues including temperature. However it seems that with some serious insulation (6" styrofoam or thereabouts) the heat generated by the electronics is enough.

BTW: Last I heard they lost the lot, make sure your phone # in printed on the box :)

EDIT: I just re read and see you've already mentioned the foam and electronics heat. Actually the thermos isn't such a bad idea, but for the construction you'd need to find one of those guys who build sailing ships in bottles.
 
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Graham O

Member
smokelight101 said:
Anyway to the picaxe portion. I plan for a picaxe or a set of picaxes to trigger the cameras, log some sensor data, and work as a TNC for a radio. The TNC takes a string of data from the gps then places it into a standardized protocol that amateur radio hobbyists use for tracking called APRS.

The questions I have.

1. Has any one have any experience with APRS or AX.25?
2. The radio uses different tones for ones and zeros. For example 1400hz for 1 and 2200 for 0 I believe for APRS. I may have the 1's and 0's fliped. Is it possible to do this with the picaxe?
3. When connecting the picaxe to the radios mic in and speaker ports what type of circuitry do you recommend? I was just thinking a resister and capacitor on the mic and a 800 to 8 ohm signal transformer on the speaker for impedance matching but I'm rather novice.

Wow that was alot. Any comments would be appreciated!!!! :)
Thanks for all the help,
Tyler Berezowsky
Click to expand...
Hello,
I'm currently working on a similar project in the UK using a Picaxe as the flight computer. In the US, you are lucky to be able to use amateur radio equipment in flight, so AX.25 is possible, but for the work involved, there are a number of micro TNC's which would make life much easier and handle all the tone generation automatically. APRS has been used a number of times in the US.
In the UK, we have to use 10mW licence free modules but using RTTY, signals have been decoded at 515km range.
With regards temperature, all the recent launches in the UK have just used the self heating effect of electronics inside the foam payload box and this keeps temperatures above -20C. If you are using a HT with data being sent every few seconds, there should be plenty of internally generated heat. But if you are worried, then a chemical handwarmer would be a cheap and convenient solution.
One big consideration is the choice of the GPS unit. There are 2 limits set which prevent them being used in ballistic missiles; a speed limit and an altitude limit. Make sure that the spec sheet for the GPS says that "either limit may be exceeded but not both" rather than "neither limit may be exceeded" (or something similar), otherwise it will cut out at 18km.

Hope that helps,

Graham
 
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testerrrs

New Member
So we launched a PICAXE based high altitude balloon last weekend - see the "High Altitude PICAXE success" thread. Project Apex and details are here: http://hexoc.com/pages/apex/apex-ii.php.

You will be seeing a minimum of -60C but no lower I would think. You would be unlucky to reach -70C.

As Graham mentioned, make sure you take note of the way the GPS chipset implements the COCOM limits as otherwise you'll be losing lock at altitude.

Lots of helpful people around for help and advice on #highaltitude on irc.freenode.net, come in and ask any questions.

*j
 
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